The proposed invention is an artificial kidney system for frequent, typically daily, hemodialysis intended to improve significantly hemodialysis therapy and prognosis, to make home hemodialysis feasible and even attractive to a much broader base of patients, and to decrease the overall cost burden for patients with chronic renal failure.
There are approximately 120,000 patients on dialysis in the United States, almost 400,000 worldwide. Most of them dialyze in hemodialysis centers and approximately 17% are on home peritoneal dialysis with less that 3% on home hemodialysis. In-center hemodialysis is performed three times per week for between two and four hours. The more "physiologic" four times per week dialysis sessions are used only with patients with severe intolerance to three times weekly dialysis, mostly related to cardiovascular instability. Home hemodialysis is also universally performed three times weekly.
It is well accepted in the nephrology community that the optimal frequency of intermittent hemodialysis for chronic renal failure has not yet been established. The first patients treated by Scribner et al., in 1959 (Scribner BH, Buri R, Caner JEZ, Hegstrom RM, Burnell JM: "The treatment of chronic uremia by means of intermittent hemodialysis: a preliminary report." Trans Am Soc Artif Intern Organs 1960; 6: 114-122) received hemodialysis at intervals of five to seven days for 20-24 hours. However, the patients manifested uremic symptoms which could only be relived by increasing the frequency of dialysis (Hegstrom RM, Murrey JS, Pendras JP, Burnell JM, Scribner BH: "Two years experience with periodic hemodialysis in the treatment of chronic uremia." Trans Am Soc Artif Intern Organs 1962; 8: 266-275). Later, in the 1960's, twice weekly dialyses were used routinely. During the 1970's, three times weekly dialyses became more popular as it was realized that the overall results were better than with twice weekly schedule. Presently, two dialysis per week are applied only in patients with well preserved residual renal function. Three dialyses per week is considered a standard schedule in the majority of dialysis centers as it seems to yield an adequate or acceptable clinical status in the majority of patients.
The amount of time consumed by transportation to and from the center, and the dialysis procedure itself, is mostly tolerable for the patients who perform three sessions per week. Consequently, only those patients who experience unbearable intolerance of body fluid volume fluctuations, and the associated symptoms, agree to more frequent (four times weekly) dialysis sessions. For home dialysis patients, more frequent dialysis than three times per week would mean more stress on the relatives who help with set-up and who monitor the patient and, of course, on the patient who does most of the work for set-up, tear-down, and cleaning.
An arteriovenous fistula, either classic or Gore-tex, is the most commonly used method of creating blood access for hemodialysis. For each dialysis session, the fistula must be punctured with large bore needles to deliver blood into, and return blood from, the artificial kidney (dialyzer). The punctures with these large bore needles are painful, even with the use of anesthetics. It is natural that the patients would like to have punctures done as infrequently as possible. Also, there is a general perception (although no proof) that frequent punctures are detrimental to the fistula longevity. Three times weekly dialysis schedule seems to be a reasonable compromise.
Last, but not least, the current Medicare reimbursement schedule for any form of dialysis is based on three hemodialyses per week done in-center. This allows the providers to maintain a small but acceptable profit margin. More frequent dialysis would mean a substantial increase in the providers' cost of treatment and result in a net loss to the provider for any patient receiving more than three treatments per week.
Existing hemodialysis systems consist fundamentally of two halves; one comprising the extracorporeal blood circuit (the blood flow path) and the other comprising the dialysate circuit or flow path. Typically, the entire blood circuit is disposable and comprises: 1) an arterial and venous fistula needle, 2) an arterial (inflow) and venous (outflow) blood line, 3) a hemodialyzer, 4) physiologic priming solutions (saline) with infusion set, and 5) an anticoagulant (heparin or citrate). The arterial needle accesses blood from the patient's fistula and is connected to the arterial blood tubing set, which conveys blood to the dialyzer.
The arterial line comprises: a pumping segment with interfaces to a blood pump (rotary or peristaltic) on the hemodialysis machine, pressure monitoring chambers including tubing which interfaces to pressure transducers on the machine to monitor the pressure pre-pump and/or post pump, inlet ports for saline and anticoagulant, and one or more injection sites for drawing blood or injecting drugs.
The hemodialyzer typically comprises a case which encloses a bundle of hollow fiber semi-permeable membrane. The blood is circulated on one side of the membrane while dialysis solution is circulated on the other, so that the two never come into direct contact. Uremic toxins diffuse out of the blood and into the dialysis solution owing to the concentration gradient. Excess water in the patent's blood enters the dialysate as a result of a pressure gradient. The membrane is made from either cellulose or synthetic polymers.
The venous line and needle carry the newly dialyzed blood away from the dialyzer and back into the patient's circulatory system via a puncture site slightly closer to the heart than the arterial needle site. The venous set is comprised of a pressure monitoring chamber with tubing leading to another pressure transducer in the machine, injection sites, and a segment of tubing which interfaces to an air detection assembly in the machine in order to prevent air emboli during treatment.
Dialysis solution is typically prepared continuously on-line in present-day machines by combining; 1) water which has first been purified by a separate water treatment system and, 2) liquid concentrates of electrolytes. Over the past decade the dialysate concentrates have evolved from a single formulation which contained acetate as the physiologic buffering agent for the correction of circulatory acidosis, to two containers where bicarbonate replaces acetate as the buffering agent, and must be kept separate due to its chemical incompatibility with calcium and magnesium. Two proportioning pumps are therefore required, the first to mix the bicarbonate concentrate with water and the second to proportion this mixture with the concentrated electrolytes to achieve the final, physiologically compatible solution.
The machine continuously monitors the pressure at the blood inlet and outlet sides of the dialyzer (by way of the pressure transducers connected to the blood sets) as well as in the dialysate circuit. Via microprocessors, the system calculates the transmembrane pressure (TMP) which determines the amount of water transmission through the membrane. These machines also have sophisticated means of measuring the amount of dialysis solution entering and dialysate leaving the dialyzer, which allows the calculation of net water removal from the patient (ultrafiltration). By electronically comparing the amount of water entering or leaving the blood with the transmembrane pressure, the system is able to control actively the water removed from the patient to a desired target previously programmed into the system. When low-water-transmission cellulosic membranes are employed, negative pressure must be generated on the dialysate side of the membrane by the machine in order to accomplish sufficient water removal. Because suction may be applied to the dialysate as it transits the dialyzer, it must first be placed under a greater vacuum in a degassing chamber so that air bubbles are not generated within the dialyzer that would cause errors in the calculation of ultrafiltration by the flow sensors and also reduce the efficiency of the dialyzer. On the other hand, when high-water-transmission, synthetic membranes are used, it is frequently necessary to apply positive pressure on the dialysate side to control the rate of ultrafiltration.
In order to understand fully the advantages of the proposed system it is necessary to also understand the existing procedures. The first step in setting up is typically to prepare the dialysate. For the concentrate of electrolytes no preparation is necessary; a hose from the machine is simply inserted into a jug just as it comes from the manufacturer. The bicarbonate, however, is most often bought as a powder because of its instability in solution, and it must first be mixed in a jug with purified water. When the concentrates are ready, the machine is turned on so that the temperature and conductivity have time to come into their safe operating ranges.
Next, all components of the extracorporeal blood circuit are unpacked, connected together using aseptic technique and threaded onto the machine by matching the respective components to their hardware interfaces. The air is primed out of the circuit by connecting sterile normal saline to the arterial tubing set via an IV administration set, and starting the blood pump on the machine. Agitation of the dialyzer is frequently necessary to remove completely the air from it, and this process can take 10-15 minutes. Some practitioners are able to both prime the circuit and rinse the blood back at the end of treatment with a single one liter bag of saline, but most often, two one-liter bags are required.
If the dialyzer is being reused, a chemical sterilizing solution will be present in the dialyzer instead of air, and this must first be rinsed out. In this case, additional steps are required. Once the bulk of the disinfectant and air are primed out of the circuit, the arterial and venous blood lines are usually connected together to form a closed loop. Thereafter, the enclosed solution is recirculated countercurrently to the dialysate, thus causing any remaining contaminants to dialyze across the membrane, into the dialysate, and down the drain. Before the patient can be connected to this primed extracorporeal circuit, the priming fluid must be manually tested for residual sterilizing chemicals (e.g. formaldehyde) by a calorimetric chemical assay to assure they are at safe levels.
At this point the arterial and venous needles are placed in the patient's blood access site, and the pump is started, causing the priming solution to the displaced into a drain container. When blood approaches the venous tubing set, the pump is stopped. The set is connected to the venous needle, and the pump speed is gradually or rapidly elevated to the prescribed value. Blood flow rates of 175-450 ml/min are typical, being limited by the needle size and access anatomy. The faster the blood flow rate, the faster the dialysis procedure can be accomplished, thereby benefitting both patient and physician (as long as water removal rates are tolerable). However, the needles, which in the past have in part determined the allowable blood flow rate, are typically 14-17 gauge, and are already pushing the tolerance of most patients.
The patient is then dialyzed for a period specified by the nephrologist. Every 15-30 minutes the patient is monitored for pulse, temperature, and blood pressure, and the functions of the machine are also noted and recorded on the patient's chart. Monitoring the patient closely, especially for blood pressure, is important because, as previously stated, a significant number of dialysis patients have very fragile cardiovascular systems and about 25% of all hemodialysis procedures result in hypotensive episodes owing to the rapidity of removing in 2-4 hours the fluid which has been accumulated over 2-3 days. Most of the patients have prodromal symptoms before hypotensive episodes but sometimes the episode occurs suddenly, without warning and patient "crashes", losing consciousness. Most of the "crashes" happen during the second half of hemodialysis sessions. The standard treatment for such blood pressure "crashes" is for the nurse of partner to open up the IV administration line connecting the saline bag to the arterial blood set and to infuse the saline in order to improve the patient's circulatory volume and bring the pressure back up. Slower ultrafiltration helps to reduce incidence of crashes. Therefore, my standard practice is to remove no more than one liter of ultrafiltration per hour. The "crashes" are less frequent if controlled ultrafiltration machines are used.
Another common occurrence during hemodialysis happens when the arterial needle sucks up against the interior wall of the blood vessel either because of the suction generated by the blood pump or because the patient changes his/her arm position. This creates excessive negative pressure in the pre-pump segment of the arterial line which, if monitored by the machine, will trip an alarm and shut off the blood pump until someone repositions the needle and/or arm and restarts the pump. This, of course, wastes time and lengthens the procedure. If the pre-pump pressure is not monitored, then as suction increases, the blood flow rate diminishes dramatically and the amount of dialysis expected does not in reality occur. Moreover, the endothelium (internal blood vessel wall lining) is damaged by suction, which predisposes to clotting and reduces fistula longevity.
At the end of the treatment, the arterial needle is removed, the saline line opened, and the pump started in order to flush the blood remaining in the extracorporeal circuit back to the patient. Most patients are very anemic (the kidneys control the production of new red cells) and, therefore, retrieval of as much blood as possible is important. Since flow is always in the same arterial to venous direction through the circuit, some practitioners will insert the arterial needle into the saline bag so the few inches of tubing between the needle and the saline infusion port will also be flushed.
When the blood is mostly out of the extracorporeal circuit, the venous needle is removed from the patient, and a compress is applied to the puncture site until it clots, which may be 10-20 minutes depending on the size of the needles and the degree of systemic anticoagulation at the end of the treatment. At this point, the needles and blood lines are discarded (in biohazard containers) as these components are rarely reused.
The majority of dialyzers are, however, reused. There are numerous procedures for reusing dialyzers both manually and automatically. In centers, special machines for simultaneous multiple dialyzer regeneration are used. Generally the steps are as follows:
1. High flow rate water flush of blood compartment. PA0 2. Force water through the membrane in dialysate compartment to blood compartment direction (reverse ultrafiltration). PA0 3. Removal of residual blood and protein by flushing blood compartment with bleach and/or peroxide. PA0 4. More water flush. PA0 5. Measurement of remaining fiber bundle volume or the ultrafiltration rate as an indicator of remaining dialyzer efficiency. PA0 6. Filing, capping, and storing the dialyzer with a chemical sterilant such as formaldehyde, peracetic acid, or glutaraldehyde. PA0 7. Documenting all of the above and assuring that there is no chance of using a reused dialyzer on a different patient.
Of course, the above procedures must be done in a biohazard environment since there is always the potential for exposure to human blood, and hepatitis and AIDS are relatively prevalent in the dialysis population. Also, the OSHA and EPA stipulate various working environment regulations owing to the hazardous sterilants and cleaning agents used.
Regeneration of dialyzers and lines may be performed on the machine. The Boag U.S. Pat. No. 4,695,385 discloses a cleaning apparatus for dialyzer and lines. The device is permanently or semipermanently connected into the dialysis machine system.
Finally, the dialysis machine plumbing must be periodically cleaned and disinfected. There are two reasons for this. The first relates to the fact that the dialysate has historically not been sterile. From the very beginning of dialysis as a therapy, the dialyzer membrane has been relied upon to be a sterile barrier between dialysate and blood. This is certainly true for whole bacteria, but concern has been growing over the past several years that with the use of synthetic membranes and their more porous structure, pyrogens, or components thereof, may be permeating these membranes and activating inflammatory processes within the patients. This may be exacerbated because the pressure gradient is frequently in the blood-to-dialysate direction when synthetic membranes are used. The second reason is that when bicarbonate containing dialysate is used, calcium carbonate inevitably precipitates and accumulates on the plumbing and must be dissolved with an acidic solution.
Clinically, three dialyses per week are associated with rapid changes in body fluid compartments and in concentrations of all dialyzable solutes. These changes are aptly called "The Unphysiology of Dialysis" (Kjellstrand CM, Evans RL, Petersen RJ, Shideman JR, von Hartizsch B, Buselmeier TJ: The Unphysiology of Dialysis: A major cause of side effects?" Kidney Int 1975; 7 (supp13); S30-S34). Many patients have enormous difficulties achieving a "dry" body weight if they accumulate three, four, or more kilograms of fluid between dialyses. Some patients, especially with heart failure, poorly tolerate even a two kilogram fluid weight gain; they are short of breath before dialysis, have muscle cramps and hypotension during dialysis, and feel "washed out" and are extremely weak, needing several hours to "equilibrate" and become functional. Serum concentration of highly toxic potassium frequently reaches dangerous levels (more than seven mEq/L), particularly preceding the first dialysis after a longer interval (weekend). To mention only a few others, calcium and pH are too low before dialysis or too high after dialysis in many patients. Empirically, in many hemodialysis units, these patients are placed on a four times weekly dialysis schedule.
Whereas the normal human kidneys function continuously to produce seamless, gradual changes in total body fluid volume and metabolic waste levels, three times weekly dialysis schedules produce tremendous, unphysiologic fluctuations which yield considerable stress on the patient's systems and undoubtedly affects their prognosis.
Historically, artificial kidneys developed according to the assumption that the machine should be very sophisticated and automated during dialysis and less so for preparation and cleansing. This assumption was valid for long and infrequent dialysis sessions. Compared to the total dialysis time the time for setup and cleansing of the machines was relatively short.
Another artificial kidney feature that has historical background is a proportioning system of producing dialysis solution and delivering it into hemodialyzer. In the early years of hemodialysis only a so called tank system has been used. The machine was provided with a large tank where purified water was premixed with dry chemicals to make dialysis solution, which was warmed and recirculated through the dialyzer dialysate path. Bicarbonate was used as a buffer; CO2 was bubbled through the solution, or lactic acid was added to the solution to prevent calcium/magnesium carbonate precipitation. With inefficient dialyzers a dialysis time of 12 hours or more was used. Warm dialysate was an excellent culture medium for bacterial growth. Long dialysis time magnified the problem. At the end of 11 hour dialysis, even with several changes of dialysis solution in the tank, bacterial growth was staggering (Twardowski Z, Bahyrycz M, Lebek R, Spett J: Zalety Stosowania plynu dializacyjnego bez glukozy w leczeniuyprezewleklej niewydolnosci nerek. (Advantages of glucose-free dialyzing fluid for hemodialysis treatment in cases of chronic renal failure.) Pol Arch Med Wewn 1973; 50: 1079-1085.). To overcome this problem a proportioning system was invented whereby the solution was being prepared ex tempore from purified water and concentrate. The concentrate contained acetate as the physiologic buffering agent because bicarbonate tended to precipitate with calcium and magnesium if present in the same concentrate.
Gradually more efficient dialyzers were designed, and time of a single dialysis session gradually decreased to 8, 6, 5, 4, 3, and even 2 hours. With very efficient dialyzers, acetate was delivered to the patient in excess of the body ability to metabolize it, which caused cardiovascular instability. An answer to this problem was to return to bicarbonate as a buffer but within an overall design of proportioning system. As mentioned before, because of chemical incompatibility of bicarbonate with calcium and magnesium, two proportioning pumps are required, the first to mix the bicarbonate concentrate with water and the second to proportion this mixture with the concentrated electrolytes to achieve the final, chemically compatible solution.
However, a short daily dialysis session of 1-3 hours offers a possibility of abandoning the proportioning system, which continues to be used out of tradition rather than a necessity. With short dialysis there is no significant bacterial growth even if the dialysis solution is premixed in a tank from water and dry chemicals with bicarbonate as a buffer, particularly if the solution flows single pass so that spent dialysate is not mixed with fresh dialysis solution. The spent dialysate that contains amino acids, vitamins, and other nitrogen products is a much better medium for bacterial growth than is the dialysis solution containing only electrolytes and glucose.
With daily, in-center hemodialysis, the time and expense now incurred by the patient and by the staff would be greatly magnified. Also, the dialysis facility's capacity for performing this number of incremental treatments would have to be increased, requiring capital expansion. It is therefore economically and logistically infeasible to do daily dialysis for everybody in-center. Consequently, the patient's home is the only practical location for this modality.
Whereas at the end of 1980 there were 5,085 such patients (9.7% of the total dialysis population), at the end of 1987 only 3,580 (3.6% of the total) patients were on home hemodialysis. The home hemodialysis population is expected to decrease further in the future because of the many disincentives to this therapy even at a frequency of three times per week. Increasing the frequency would only exacerbate most of the following disadvantages:
a: Current equipment is big, complicated, intimidating, and difficult to operate, requiring a very long time for training. Also, both partner and patient must be trained and this represents a major expense to the medial provider.
b: Complication of equipment engenders reliability issues. If a hemodialysis system breaks down in a patient's home, no dialysis is possible until it is repaired.
c: It is currently very difficult for home hemo patients to travel since the present systems are in no way portable.
d: If the bicarbonate component of the dialysate is used in powdered form, it must be mixed and inspected by the patient.
e: Supplies require a large storage space.
f: There is a high initial investment in the dialysis equipment, the water treatment system, and their instillation with low utilization (one patient only) compared to in-center use where the systems are used on many patients.
g: There is little or no possibility for reuse of supplies, providing less economic incentive to the medical sponsor.
h: a partner is required to insert fistula needles and monitor emergencies.
i: Considerable time is involved for setup, priming, tear down, and cleaning.
j: The water treatment system must also be cleaned/disinfected periodically.
Because of the above mentioned disincentives, only highly motivated patients and partners undertake the drudgery of home hemodialysis.
Development of a transcutaneous blood access catheter not requiring needle punctures for each dialysis is currently underway and is described in Twardowski ZJ, Van Stone JC, and Nichols WK: Multiple Lumen Catheter for Hemodialysis, as described in U.S. Pat. No. 5,209,723, assigned to the Curators of the University of Missouri. Such an access device further opens the feasibility of daily hemodialysis.